It is well known that eating too many carbohydrates can lead to weight gain.

This is a particular problem with simple carbohydrates - those found in processed foods and white flour.

As these carbohydrates are digested, the starchy part is converted directly into sugar, and any that is not used is stored as fat.

Many people reduce their carbohydrate intake to cut the amount of fat stored. Doing this also helps to reduce the carbohydrate cravings linked to weight gain.

Sugar (or carb) cravings are thought to be a key factor in weight gain. When blood sugar levels are high, insulin is released by the pancreas to bring down the sugar levels.

But in those who eat a lot of sugar, or older people who have less effective insulin reactions, too much insulin is released, pushing the blood sugar levels too low.

This causes sugar cravings, which the body mistakes for hunger pangs.

When you eat to satisfy these pangs, your sugar levels rise and the whole cycle starts again. Many overweight people have erratic or high sugar levels. This makes them feel hungry and leads to bingeing.

Products to block carbohydrate digestion have been available in the UK for several years, both via prescription and over the counter.

These usually work by breaking carbohydrates down into disaccharides, a form of sugar that doesn't convert to fat. Unfortunately these disaccharides ferment with bacteria found naturally in the gut, causing gas and diarrhoea as they pass through the digestive tract.

DEcarb, which is the first carbohydrate blocker to carry an EU Certified Medical Device Status, claims not to produce these unpleasant side-effects.

It is made from an extract of the white kidney bean called phaseolamin. Carbohydrates are usually broken down by an enzyme known as alpha amylase, produced in the pancreas.

Phaseolamin reduces the effectiveness of this enzyme, preventing carbohydrates being converted into sugar. This means side- effects are virtually eradicated, although some people may suffer flatulence for a few days as the stomach adapts.

DEcarb contains a very high concentration of phaseolamin. In a small study carried out at the University of Scranton, Pennsylvania, a 1.5g tablet cut the amount of carbohydrate absorbed in a meal by up to 66 per cent.

'To lose weight and keep it off, there is no alternative but to make significant lifestyle changes,' explains Dr Shivakant Upadhyaya, of Global Goldshield Consumer Health, which makes the product.

'DEcarb can help you only for as long as you take it and, of course, you can't take it for ever. Having said that, we know that one of the benefits is that it reduces carbohydrate cravings.'

But Dr Carel le Roux, an obesity specialist at Imperial College London, says any product that can reduce carbohydrate consumption so dramatically should be treated with caution.

'Reducing carbohydrates in an overweight person's diet can be very helpful to lower blood sugars,' he explains.

'But a product that can lower absorption of carbohydrates by 66 per cent may have significant side-effects, as the unabsorbed food would have to be excreted with smelly consequences.

'The body may sense through the upper part of the gut that carbohydrates were consumed, but if it is not absorbed the body may increase the cravings that lead to over-consumption.

'Most worryingly, what happens after the treatment stops? The body is likely to rebound, regain the weight lost plus extra weight, resulting in yo-yo dieting.

'If you can't take DEcarb long term it should be avoided because the risk of gaining weight in the medium to long term may be very significant.'

So, could eating more of the beans themselves help you lose weight in the same way?

It is unlikely - the amounts you would need might make you unacceptable company. However, nutritionists recommend beans as a good source of fibre, which will protect against some cancers.